1. Field of the Invention
The present invention relates to an electric rotary machine for vehicles such as passenger cars and trucks, in particular to an electric rotary machine having an improved rotor structure comprised of permanent magnets and pole cores with claw magnetic pole parts.
2. Description of the Related Art
Various types of electric rotary machines are mounted to vehicles. For example, Japanese patent laid open publication NO. JP H09-131030 has disclosed an alternate current (AC) generator or a vehicular alternator for a vehicle. The conventional AC generator has permanent magnets placed between adjacent claw magnetic pole parts. The claw magnetic pole parts are annularity arranged on the outer peripheral surface of a Lundell type rotor. The claw magnetic pole parts are alternately faced to each other. The structural combination of the claw magnetic pole parts and the permanent magnets prevents leakage of magnet flux from the area between the adjacent claw magnetic pole parts, and thereby increases the amount of effective magnet flux.
In addition, a flange part is formed at the outer periphery of each of the claw magnetic pole parts in the Lundell type rotor in the AC generator having the above structure in order to fix the permanent magnets in the diameter direction of the rotor against the centrifugal force generated when the Lundell type rotor rotates. Therefore the presence of the flange parts prevents the permanent magnets from being moved toward the outer diameter direction by the centrifugal force generated when the rotor rotates.
However, the conventional AC generator of the above structure has a drawback because no permanent magnet is placed between the flanges of the adjacent claw magnetic pole parts which are annularity arranged on the Lundell type rotor. Therefore the above structure of the conventional AC generator allows the leakage of magnet flux through the area between the adjacent flanges of the adjacent magnetic claw pole parts, and thereby decreases the amount of electric power of the AC generator. That is, the more the thickness of each of the flanges formed on the claw magnetic pole parts is decreased in the diameter direction (or radius direction) of the rotor, the more the anti-centrifugal strength of the flanges is decreased. In other words, a thin flange of the claw magnetic pole part has a weak anti-centrifugal strength.